Fire retardant polymer resin

ABSTRACT

Flame retardant polymer resins formed by an acid condensation reaction from a mixture of resorcinol and furfural with a molar excess of the aldehyde. In one particular embodiment the resin is formed of a mixture of two prepolymer solutions with at least a boric acid catalyst, one or both of the prepolymer solutions being an acid-condensation reaction product of resorcinol and furfural with excess aldehyde functionality, or one of the prepolymers being a mix of substantially unreacted resorcinol and furfural with a slight molar excess of aldehyde.

This application is a division of our copending application Ser. No.73,218, filed Sept. 7, 1979 now U.S. Pat. No. 4,275,170 for FireRetardant Polymer Resin, the latter in turn being a continuation-in-partof copending application Ser. No. 58,567, filed July 18, 1979, nowabandoned.

The present invention relates generally to flame-retardant polymerresins, and in particular to novel synthetic polymer resins which areself-extinguishing and non-punking upon exposure to flames. Theinvention also contemplates novel processes for producing novelsynthetic polymer resins having the aforesaid characteristics. Theinvention has particular utility in connection with the preparation ofsynthetic polymer resins in foam form for use in thermal insulationsystems and will be described in detail in connection with such utility.However, the invention is not limited to the production of polymer foamsas will become clear from the description following.

Various synthetic polymer resins are known in the art and have achievedsubstantial commercial utility. By way of example, polymer foams basedon polyurethane and on polystyrene formulations have achievedsubstantial use in thermal insulation systems. Polyurethane-basedpolymer foams offer certain processing advantages in that they may befoamed in situ, and may also be cast in structurally self-supportingsheet or panel form. On the other hand, polyurethane andpolystyrene-based polymer foams per se are highly flammable. In order toreduce flammability of polyurethane and polystyrene-based polymer foams,it has been proposed in incorporate phosphorus and halogen containingadditives into the foam formulations. While modifying polyurethane andpolystyrene based polymer foams in accordance with the foregoing mayrender the resultant polymer foams self-extinguishing, the resultantpolymer foams generally produce toxic smoke when exposed to open flame.Moreover, some pyrolysis products of polyurethane and polystyrene-basedpolymer foams also are flammable, and may cause flash fires if theycollect in a closed area. These and other problems and disadvantageshave restricted wider commercial use of polyurethane and polystyrenebased polymer foams in thermal insulation systems.

Polymer foams based on polyimides, polybenzimidazoles,polyphenylquinoxilines, pyrrones, and other highly aromatic polymermaterials have also been proposed for use in thermal insulation systems.While polymer foams based on such highly aromatic polymer materials aresaid to offer extremely high flame retardancy characteristics, none ofthese polymer foams is believed to have achieved any substantial degreeof commercial utilization due to high raw materials cost. Also, limitingcommercial utilization of such polymer foams are the requirements forspecial processing techniques and apparatus for producing the foams.

Polymer foams based on ureaformaldehyde and phenolformaldehyde have alsobeen proposed for use in thermal insulating systems, and have achievedsome degree of commercial utilization. Polymer foams based onureaformaldehyde and phenolformaldehyde are relatively inexpensive, andcan be foamed in situ using commercially available foaming apparatus.Also, polymer foams based on ureaformaldehyde exhibit good mechanicalproperties but generally generate relatively large quantities of smokeupon exposure to flame, and such polymer foams also are susceptible todegradation in the presence of moisture. Polymer foams based onphenolformaldehyde also exhibit good mechanical properties, and inaddition generally are stable in the presence of moisture. Moreover,polymer foams based on phenolformaldehyde exhibit relatively low flamespread and smoke generation on exposure to flames. On the other hand,polymer foams based on phenolformaldehyde generally suffer fromso-called "afterglow" or "punking", a phenomenon that causes the foam tobe consumed by flameless oxidation after exposure to a fire. While anumber of investigators have proposd various solutions of makingphenolic foams non-punking, none of such solutions is believed to beentirely satisfactory. Many polymers utilized in foam formulationsemploy alkali or alkaline earth materials as polymerization catalystsand it is believed that such materials may in fact contribute tocombustion of the polymer.

It is thus a primary object of the present invention to provide new andimproved synthetic polymers which overcome the aforesaid and otherproblems of prior art. Another object of the present invention is toprovide new and improved polymer foams for use in thermal insulationsystems, which foams are characterized by low flame spread, low smokegeneration, and resistance to afterglow or punking. Still another objectof the present invention is to provide new and improved polymer foams ofthe type above-described which exhibit good mechanical properties andresistance to moisture. Still another object of the present invention isto provide a novel process for producing polymer foam materials havingthe aforesaid characteristics.

The invention accordingly comprises the processes involving the severalsteps and relative order of one or more such steps with respect to eachother, and the materials and products possessing the features,properties and relations of elements which are exemplified in thefollowing detailed disclosure and the scope of the application of whichwill be indicated in the claims.

Generally, in the practice of this invention, new phenolic resins basedon phenol-aldehyde are derived as the reaction product of a polyhydricphenol with an aldehyde polymerized with a catalyst. In one form, theresins are derived from a two-part formulation comprising: Part (A) is astable, low viscosity liquid, low molecular weight prepolymer in whichis an acid-condensation reaction product of an aldehyde and a polyhydricphenol, containing excess aldehyde functionality, and Part (B) anotherlow viscosity liquid which can either be (1) an acid-condensationreaction product also of an aldehyde and a polyhydric phenol, containingexcess aldehdyde functionality or (2) another low viscosity liquid whichis a substantially unreacted mixture of aldehyde and polyhydric phenol,containing aldehyde in molar excess. In the two part formulation, Part(A) also contains an active polymerization catalyst, a solid acid thatrequires water for initiation, and Part (B) contains a polymerizationcatalyst which comprises an inorganic Lewis acid containing water ofhydration, such as boric acid or a boric acid complex. Both Parts (A)and (B) of the formulation are substantially unreacted until the twoparts are mixed together.

In a preferred embodiment of the invention the aldehyde comprisesfurfural and the polyhydric phenol comprises resorcinol.

Still other objects and many of the advantages of the present inventionwill become clear from the description following.

As used herein the terms "Part (A)" and "Part (B)" are employed solelyfor convenience to distinguish the initial aldehyde/phenolacid-condensation reaction product part of the two-part formulationcontaining active polymerization catalyst on the one hand, from thealdehyde/phenol mixture (reacted or unreacted) part of the formulationon the other hand.

In preparing the novel phenolic resins in accordance with the presentinvention, the first step is to separately prepare the two formulationsParts (A) and (B). To prepare Part (A), an aldehyde and a polyhydricphenol are mixed together in a ratio of between about two and four molesof the aldehyde for each mole of polyhydric phenol. To this mixture isadded a relatively small amount (e.g. 0.1 to 1.0 weight percent) of amineral acid such as 10% HCl solution in water. The acid catalyzes thecondensation polymerization of the aldehyde and the phenol to form arelatively low molecular weight linear polymer having excess aldehydefunctionality. This polymer is a relatively stable, low viscosityliquid. Part (B) of the formulation is prepared either identically toPart A, or by mixing an aldehyde and a polyhydric phenol in a ratiobetween about one and two moles of the aldehyde for each mole ofpolyhydric phenol. Preferably, but not necessarily, the aldehyde and thepolyhydric phenol in Part (A) of the formulation, and the aldehyde andthe polyhydric phenol in Part (B) of the formulation, are chemicallyidentical. The resulting mixture (Part B of the formulation) is arelatively stable solution of the polyhydric phenol in the aldehyde,little or no reaction occuring upon mixture of the aldehyde and thepolyhydric phenol unless a mineral acid catalyst is added as would bethe case where Part B is prepared in the same manner as Part A.

The next step is to incorporate selected catalysts into Parts (A) and(B) of the formulation. A feature and advantage of the present inventionresides in the selection of, and distribution of a condensationpolymerization active catalyst in one part of the formulation and apolymerization initiation catalyst in the other part of the formulationsuch that both Parts (A) and (B) of the formulation remain stable, andrelatively unreactive until they are mixed. The polymerization activecatalyst is added to Part (A) of the formulation, while thepolymerization initiation catalyst is added to Part (B) of theformulation. The polymerization active catalyst added to Part (A) is asolid organic acid which is water soluble, but is substantiallyinsoluble in Part (A) of the formulation. The acid in solid form isinactive as a polymerization catalyst.

The polymerization initiation catalyst added to Part B comprises boricacid. The boric acid polymerization initiation catalyst serves severalfunctions, but primarily acts as an activator to initiate rapidpolymerization once Parts (A) and (B) of the formulation are mixedtogether. Also, the boric acid is believed to undergo chemical reactionwith the low molecular weight polymer of the formulation Part (A) andthereby becomes an integral part of the final cured polymer network.

Upon polymerization, the following reaction is postulated to occurbetween the boric acid and the resorcinol in Part (B) and also withavailable resorcinol hydroxyl groups: ##STR1##

The degree to which Reaction I occurs and the actual number offunctional sites involved in chemical reaction is not known. However, itis also believed that the boric acid may also react with free resorcinolor resorcinol that has been reacted to form the low molecular weightpolymer product of Part (A).

As mentioned supra, Part (A) and Part (B) of the formulation arerelatively stable liquids until they are mixed together. However, onceParts (A) and (B) are mixed together with the catalyst, a condensationpolymerization commences, and the solid boric acid partially dissolvesin water produced by the condensation polymerization reaction, and thusbecomes active so as to catalyze complete cure. One skilled in the artwill recognize the use of a solid boric acid catalyst in accordance withthe present invention provides the two fold functions of (1) controllingrelease of active acid catalyst whereby to maintain control over theexothermic condensation polymerization reaction of the polymer, and (2)providing sufficient catalyst release to insure complete cure of theresin over a period of time which may be varied. Polymerizationgenerally is initiated within about 60 and 180 seconds following mixingof the formulation Parts (A) and (B), depending on the initialtemperature of the materials and catalyst concentration. Complete curingat room temperature generally occurs within several hours thereafter.Polymerization rate and degree of polymerization can be varied byvarying the acid catalyst in Part (A), amount of acid catalyst presentin Parts (A) and (B), particle size of acid catalyst (solid acids)and/or degree of hydration of the acid catalyst (solid acids).

The two-part prepolymer compositions are separately formulated, and aremaintained isolated from one another until the polymer is to be formed.The novel polymer material of the present invention may be formed as afoam by incorporating known foaming agents such as polyhalogenatedsaturated fluorocarbons in known manner and employing known productionequipment, and may be cast as foamed board stock on continuousproduction equipment, or the polymer materials may be foamed in situ.Alternatively, the polymer material of the present invention may beformulated in appropriate weight for use as a fire retardant coating, ina laminate or with ablative materials as will be described in detailhereinafter.

More specifically, the aldehyde compounds used herein comprise a lowmolecular weight unsaturated aldehyde such as furfuraldehyde (furfural)and mixtures of furfural and paraformaldehyde. The polyhydric phenolcomprises resorcinol and substituted resorcinols such as methylresorcinol. Resorcinols have been found to provide polymers which arehighly crosslinked and tend to be thermally stable. Methyl resorcinolused in the present invention tends to produce a stronger, less friablepolymer foam than resorcinol. Other phenols may be combined, such asphenol, metacresol, orthocresol, 3,5-dimethylphenol and the like butwith at least a minor amount (e.g. 25% or more by weight of thepolyhydric phenol present. To prepare prepolymer Part A, a mixture ofaldehyde and polyhydric phenol is made, generally in a molar ratio ofabout three to one. Then a small amount, e.g. about 0.5 weight % ofdilute inorganic acids such as 10% HCl solution in water is added. Anexothermic reaction occurs resulting in the condensation reactionbetween the aldehyde and the phenol. Since the aldehyde is insubstantial molar excess, the condensation reaction product is a liquidlow molecular weight prepolymer with excess aldehyde functionality. Theresulting product is a relatively low viscosity liquid. An importantfeature and advantage of the present invention is to prepare thisportion of the prepolymer prior to the polymer foaming operation. Bypreparing the prepolymer in this manner much of the exothermic reactionoccurs prior to actual foaming. This permits foaming to be carried outsuch that the polymer product may be reproduced in a controllable anduseful manner. A small amount of solid, water soluble organic acid cannow be added as a catalyst.

Part (B) of the prepolymer can be a pre-reacted mixture of the aldehydeand phenol comprising the same molar ratio as Part A, or a substantiallyunreacted mixture of aldehyde and phenol, with the aldehyde in a slightmolar excess, e.g. typically the aldehyde is in molar excess relative tothe phenol in the range of about 1.25:1 to 1.5:1. The boric acidcatalyst is now added. The resulting mixture comprises a low viscosityliquid.

Formulations have also been developed that incorporate furfuryl alcoholin either Part A or Part B or both. Furfuryl alcohol monomer behaveschemically in a manner similar to the initial reaction product betweenphenols and aldehydes which is also an alcohol. Therefore, from thestandpoint of chemical stoichiometry of the resin system, one mole offurfuryl alcohol is the equivalent of one mole of a phenol and one moleof an aldehyde.

Formulations of up to 50 weight % furfuryl alcohol in the overall resinhave been prepared. Approximately 9.0 weight % is preferred from thestandpoint of processing ease and final foam properties. For a 2.65lb/ft³, foam compressive strength was increased from 9.0 psi to 16 psiby addition of 9.0 weight % of furfuryl alcohol.

The two-part prepolymer system is now ready for use in preparation ofpolymeric materials of the present invention, particularly for processesof preparing foams, in which processes rapid polymerization time isimportant to preserve the cellular foam structure. The approach used isto prepare a two-part formulation in the above manner resulting instable unreactive prepolymer mixtures. If desired, a foaming agent suchas one of the Freons (trademark of E. I. DuPont Co. for certainfluorocarbon liquid/gasses refrigerant) may be added to a mixture of thetwo prepolymers for producing a polymer foam. Alternatively, where thepolymeric material is to be employed as a coating, in a laminate or in acomposite ablative material, the two parts prepolymers are mixedtogether without blowing or foaming agents and with, if desired, inertfillers. Also, in such case, the two part system may not be necessaryinasmuch as rapid polymerization is not required.

As mentioned supra an important feature of the present invention is toprepare the two-part prepolymer system in such a manner that much of theheat of reaction is produced prior to the actual polymer formation.Still another important feature of the present invention resides in theuse of certain solid, water-soluble organic acids as the polymerizationcatalyst in the two-part system. By employing an organic acid ininactive solid form, the latter will remain solid in the prepolymeruntil dissolved in water of condensation produced during polymerization.That is to say, the acid becomes active only as it dissolves inavailable water. This permits controlled release of active acid catalystwhereby control is maintained over the exothermic polymerizationreaction of the prepolymers and thereby provides sufficient catalystrelease to insure complete cure of the foam over a period of severalhours after initial preparation of the foam. Generally, thewater-soluble, solid, organic acid catalyst useful in accordance withthe two part system of the present invention are acids such as citric,fumaric, itaconic, malic, maleic, oxalic and tartaric acids. Liquidorganic acids such as acetic and acrylic can be used, but are notpreferred because of their reactivity. Moreover, the degree and rate ofpolymerization can be varied by varying the particular solid organicacid catalyst used, amount of that acid catalyst, particle size of thatacid catalyst and the degree of hydration of that acid catalyst. Forexample, polymerization of the two-part prepolymer resin system can bemade to proceed faster if the solid organic acid catalyst has a smallparticle size, is highly soluble in water and anhydrous initially. Ingeneral the higher concentration of catalyst present, the faster andfurther polymerization will occur. Catalysis without heat by theseorganic acids requires the presence of boric acid.

In addition to solid organic acid catalyst materials, certain mineralacids can be employed as polymerization catalysts in accordance with thepresent invention. Among such acids are phosphoric acid, phosphorousacid, sulphuric acid, hydrochloric and organic acid phosphates such asbutyl phosphate and the like. However, mineral acids generally are moredifficult to control and thus generally are not preferred catalystsmaterials except for coatings, laminates and ablative composites,particularly in the one part system of the present invention.

As noted, an important feature of the two part system of the presentinvention is the addition of boric acid to Part (B) prepolymer. Thepresence of boric acid in the prepolymer and the resulting polymerprovides heat absorption in a fire environment due to release of largeamounts of water of hydration available in the boric acid. Boric is aLewis acid and tends to catalyze char formation during pyrolysis whichin turn reduces the quantity of combustion gases which might otherwisebe generated when the polymer material is exposed to flame. Boric acidis also believed to be coreactive with the prepolymer thereby enteringinto the polymer structure. Finally, boric acid is a glass-formingmaterial, and such boric oxide glass can melt and thereby add oxidationprotection to the charred foam in a fire environment.

The degree to which boron incorporation occurs and actual number offunctional sites involved in the polymerization reaction inclusion ofboron is not known; however, it is believed that boron reaction may alsooccur on free phenol or phenol that has been reacted into theprepolymer. The boric acid is also believed to function as an activatorto initiate polymerization after Parts (A) and (B) of the prepolymersare mixed together. This activation is believed to be related toreaction of boric acid with the polymer and its role as a Lewis acid.Thus, if Parts (A) and (B) of the prepolymer are mixed together and thefoam prepared without the presence of boric acid, the system isessentially nonreactive and polymerization does not commence. On theother hand, the addition of a small amount of boric acid has been foundto immediately activate the system causing polymerization to proceed.Polymerization can also proceed without boric acid if a strong mineralacid such as HCl is added; however, polymerization under theseconditions is difficult to initiate unless relatively large amounts ofacid are required. Once such polymerization is initiated it is veryexothermic and difficult to control, hence is used herein primarily toform ablative materials from a single-part system of mixed furfural andresorcinol.

Because the nature of some of the primary ingredients used to synthesizethe two part resin system are acidic, self-polymerization will tend tooccur gradually over a period of time. It has been found that the use of"acidic" or "basic" inorganic powder fillers can be used to eitheraccelerate self-polymerization or to retard it. As an example, theincorporation of as little as 5 wt % calcium sulphate hemihydrate willaccelerate self-polymerization, while the addition of 5 wt % commercialPortland Cement will retard self-polymerization. Various fillers such asmica, wollastonite, calcium silicate, titanium dioxide, and aluminumtrihydrate have also shown similar behavior.

It is evident that the use of "acidic" and "basic" inorganic fillers canbe used to either prolong the storage or shelf life of the prepolymers,or can be used to prime the activity of prepolymers prior to acidcatalyzation in order to control final polymerization and the resultingproperties of the foam.

The polymeric materials resulting from mixing prepolymers Parts A and Bin the presence of the boric acid catalyst, if produced in the presenceof a foaming agent, may be used as thermal insulating systems.Alternatively, by omitting the blowing agent and adjusting catalystconcentrations, the same two-part polymer system may be employed as afire retardant resin coating, or in a laminate or in conjunction with anablative composite material, although for the latter, a single-partsystem is less expensive.

For example, another method of producing a fire retardant resin,particularly useful for forming ablative materials, is by a single partsystem exemplified by the direct reaction of a phenol and an aldehdye inthe presence of an acid catalyst. The preferred approach is to form asolution of resorcinol in furfural in molar ratios ranging from about0.5 to 1. This solution is stable and essentially nonreactive until thecatalyst is added. Any of the acid catalysts or catalyst combinationsdescribed in the previous disclosure are applicable. The resultingpolymer may lack the advantages conferred by the boric acid if thelatter is not used, but does constitute an excellent ablative material.

This approach is preferred for use in formulating fire retardantcoatings and ablative composites. In producing these coatings andcomposites, additives such as pigments and refractory fibers arecombined with the chemical solution. When these additions are properlydispersed, the system is suitable for application. A catalyst system isthen added to initiate the polymerization reaction leading to a curedcoating or composite. The catalyst is selected to provide a relativelyslow ambient temperature polymerization without excessive exotherm.

After addition of the catalyst, the formulation can be cast, sprayed orspread depending on the configuration and/or use of the final product.Polymerization to form a cured product occurs at ambient temperatureover a 24-48 hour period. Heat can be used to accelerate thispolymerization.

The following examples, which are illustrative and not meant to belimiting, are given to provide an additional description of theinvention. In order to test for fire resistance the resulting polymericcompositions were exposed to the cutting flame of an oxyacetylene torch.

EXAMPLE I

A flask equipped with an agitator was charged with a mixture of furfuraland resorcinol in a mole ratio of 3.6 to 1. Approximately 2 weightpercent of 10% HCL solution in water was added. The contents wereobserved to heat up, and the solution was continually stirred for ashort period of a few minutes to provide the condensation reactionproduct between furfural and resorcinol, hereinafter called Part A.

A second flask equipped with an agitator was charged with a mixture offurfural and resorcinol in a molar ratio of 1.3 to 1. The resorcinol wasobserved to dissolve in the furfural to provide Part B.

To 168.3 grams of the prepolymer condensation reaction product of Part Awas added 10 grams of tartaric acid. To 152.0 grams of the mixture offurfural and resorcinol prepared as Part B is added 55 grams of boricacid, 50 grams of Freon 113 (trichlorotrifluoroethane), and 9 grams of asurfactant to aid foaming (UCC5340 non-ionic silicon available fromUnion Carbide Corporation).

To produce polymeric foam, Part A of the preparation and Part B of thepreparation are combined in a ratio of 1 to 1.45 parts by weight andmixed by a motor driven stirrer. Foaming is seen to occur within about60 to 180 seconds at ambient temperture. However, several hours arerequired before complete cure is obtained. The resulting product is arigid foam of approximately about 1.8-2.8 pounds per cubic foot density.The foam is tested for flammability by subjecting the foam product tothe flame of the torch. No visible smoke to detectable odor is observed,and no sign of combustion or flammability is noted. Additionalproperties of this foam are given in the following table.

The foam, tested for physical properties and flammability has thefollowing characteristics:

    ______________________________________                                        Nominal Density                                                                             1.8-2.8 lb/ft.sup.3                                             Closed Cell Content                                                                         30%                                                             K-Factor (initial)                                                                           ##STR2##                                                       water Vapor                                                                   Permeability  70 Perms                                                        Water Absorption                                                                            3.6% by Volume                                                  Compressive Strength                                                                        9 psi (2 lb/ft.sup.3)                                           (parallel to rise)                                                                          19 psi (2.8 lb/ft.sup.3)                                        Flexural Strength                                                                           7.6%                                                            (load deflection @                                                            75% of compression                                                            load)                                                                         Flammability Test                                                                           Flame Spread  Heat Evolution                                                  Factor        Factor                                                          1             1.1                                                             Flame Spread                                                                  Index                                                                         1                                                               Smoke Test (NBS)                                                                            Specific Optical Density                                                               90 sec    4 min                                                    Non-Flaming                                                                              0         0                                                        Flaming    0         1                                            ______________________________________                                    

EXAMPLE II

Prepolymer foam resin is prepared by mixing 1,273.9 g furfural, 627.5 gresorcinol, 100.0 g surfactant and 5.7 g of acid catalyst in a reactionvessel. The catalyst may be a hydrochloric acid solution such as inExample I. However, a preferred catalyst consists of a mixture of 10parts by weight organic acid phosphate such as PA-75 (a phosphoric acidderivative sold by Mobil Oil Co.) to 90 parts furfural. After mixing, aslow condensation reaction occurs between the furfural and theresorcinol. From this same prepolymer mixture, Part (A) and Part (B) areprepared. Part (A) consists of 1,012.1 g of prepolymer, 198.3 g tartaricacid, and 406.7 g of freon 113. Part (B) consists of 995 g prepolymerand 608 g boric acid.

To produce a foam, equal volumes (1:1) of Part (A) and Part (B) aremixed together using a high shear laboratory mixer. Foaming is seen tooccur within about 60 to 180 seconds at ambient temperature. As inExample 1, several hours are required before complete cure is obtained.The resulting product is a rigid foam of approximately 2 to 3 pounds percubic foot density with physical properties and fire retardantproperties similar to the foam described in Example 1.

EXAMPLE III

To prepare fire retardant coating, prepolymer Part A is formed by mixingtogether the following by weight: furfural 43%, resorcinol 10.5%, acetal(Formvar 15/95E) 3.5%, titanium dioxide 31.5%, aluminum trihydrate10.5%, surfactant DC 193 1.0%, with a trace of 85% phosphoric acid toserve as a catalyst. Titanium dioxide is added simply as a pigment tochange the normal black color of the cured resin to a battleship gray.The acetal is added to provide toughness and flexibility to the curedresin coating when applied to substrates such as aluminum and steel,without sacrificing fire retardancy.

Prepolymer Part B is formed by mixing together the following by weight:furfural 37%, resorcinol 34%, boric acid 29%.

A formulation consisting of 63.8% Part A and 36.2% Part B from thisexample is used to coat mild steel plates measuring 1/4"×12"×18" using anylon paint brush. The coatings will gel within one to two hours and arethen heat cured for several hours at 150° F. When the coatings areexposed to the flame of an oxyacetylene torch they will not burn orpropagate a flame.

EXAMPLE IV

The preparation of fire retardant laminates using fiberglass clothembedded in a cured resin matrix is accomplished by preparing the resinin the same manner as the coating resin described previously in ExampleIII with the exception that no pigments are used. However, the use of apigment is technically feasible. As with the coatings, no blowing agentis used and the acid catalyst is modified to suit the particularrequirements for polymerization of the laminate-resin structure.

Once again the incorporation of an acetal such as Formavar 15/95E isbelieved to improve the adhesion of the resin to the surface of thefiberglass, and the resulting laminate will exhibit no burning or flamepropagation when subjected to the flame of the torch.

EXAMPLE V

The preparation of a fire retardant ablative composite material isaccomplished from a single part mixture in the following manner: 1,641 gof furfural are mixed with 867 g of resorcinol using a high shear mixer.To this resin mixture 418 g of a refractory type fiber are added whilethe resin is being mixed. Ideally a Banbury or Hobart type mixer shouldbe used for beating the fibers into the resin mix to minimize breakdown.These fibers may be carbon, graphite or silica; however, graphite fibersare preferred.

The resin-fiber mixture can be catalyzed by any of the previouslymentioned acids in sufficient quantity. However, a preferred catalystconsists of a mixture of 25 parts by weight of an phosphoric acidderivative such as PA-75, to 75 parts furfural. Typically up to 50 ml ofthe catalyst mixture will initiate a controllable room temperature curewithin 24 hours. In this example, the resin/fiber batch is transferredinto a gallon metal container and the catalyst is added. Uniform mixingof the catalyst and batch is achieved by immediately closing the metalcontainer and shaking it for approximately five minutes on a gyratorytype paint shaker. Alternatively, larger batches may be catalyzed usinga rotating mortar mixer, or a Banbury or Hobart type mixer.

Such an ablative material as described above can be cast into mouldedshapes using vibrating equipment or manual tamping of the mould. Thedensity of the finished part can vary from 80 to 100 lbs/ft³ dependingon the amount of entrained air that is removed during the castingprocess.

EXAMPLE VI

In another example of an ablative material to the same mixture asdescribed in Example V, up to 10PHR high surface area carbon black isadded prior to catalyzation . The carbon black absorbs excess resinduring casting, minimizing resin run-out. In addition, the carbon blackimparts a thixotropic nature to the resin allowing it to be troweledonto vertical surfaces without slumping or falling off.

Since certain changes may be made in the above method without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted in an illustrative and not in a limitingsense.

What is claimed is:
 1. A flame retardant polymer resin preparedaccording to the method comprising the steps ofreacting moities of afirst aldehyde and first phenol in the presence of a mineral acid insufficient proportions to provide an acid-condensation reaction productin the form of a relatively low molecular weight, low viscosity, liquidlinear polymer having excess aldehyde functionality, said first aldehyebeing selected from the group consisting of furfural and mixtures offurfural and paraformaldehyde, said first phenol being selected from thegroup consisting of metacresol, orthocresol, 3,5 dimethylphenol,resorcinol and substituted resorcinols; mixing moities of a secondaldehyde and second phenol to provide a solution of said second phenolin said second aldehyde, which solution is separate from said reactionproduct and contains said aldehyde in molar excess, said second aldehydeand second phenol being selected from the same groups as said firstaldehyde and first phenol; adding to said reaction product a solid,organic, watersoluble acid as a polymerization active catalyst; addingto said solution an inorganic acid polymerization catalyst containingwater of hydration, said inorganic acid being selected from the groupconsisting of boric acid and boric acid complexes; and reacting amixture of said reaction product and said solution in the presence ofsaid catalysts to produce condensation polymerization thereof into saidresin.